Hydrogen tube



March 8, 1949.

H. H. CARY ETAL HYDROGEN TUBE Filed D60. 29, 1945 INVEN TOPS HENQY CARY5/ WARREN f? BAXTER HARP/5, /ECH, FOSTER (ff/A RRIS QFAQOZ FOR THE FIRMA TTORNE vs Patented Mar. 8, 1949 HYDROGEN TUBE Henry 1!. Gary,Alhambra, and Warren 1'. Baxter, Pasadena, Calif alslgnors to NationalTechnical Laborateries, Pasadena, Calif.\a corporation of CaliforniaApplication December 29, 1945, Serial No. 638,062

1 .16 Claims. Our invention relates to gas-filled electron tubes and,more particularly; to a. novel hydrogren tube of small size and longlife particularly suited for use in spectrophotometry where it isdesirable to have a concentrated source of continuous ultra violetradiation in the region of about-300450 miilimicrons but without stronlines in the spectrum within this. band. The invention is primarilyconcerned with the so-called low voltage or thermionic hydrogendischarge tubes in which voltages ranging from about 50- 100 aresuflicient to maintain the discharge.

Heretofore. hydrogen tubes of this type have been quite bulky and opento many objections. The most common construction provides a relativelylarge glass envelope having a. quartz or fused silica window sealedacross an aperture of the glass for transmitting the ultra violetradiation from the tube. Within the glass envelope, such tubes provide ametallic enclosure surrounding the cathode and having a small openingthrough which the electron stream moves on its way to an arcuate anodepositioned between the enclosure and the glass envelope and having alarger opening disposed between the window and the small opening of theenclosure. The interior of the glass envelope is filled with hydrogenandelectrons from the heated cathode move outward through the small openingunder the attraction of the positively-charged anode.

Attempts to reduce the size of such conventionally-constructed hydrogentubes have heretofore resulted in an unexplained and very substantialdecrease in tube life, accompanied by rapid darkening of the windowand/or by reduction in intensity of the discharge itself.

It is an object of the present invention to provide a small hydrogentube of long effective life. By a long-lived tube we have reference to ahydrogen tube having a useful life of at least 200 hours. According tothe teachings of the present application, the life can be made over 1000hours, a life of 3000 hours being quite common.

We have found that very substantial and unexpected advantages arise froma. general reversal of the customary position of the cathode and ani-de,and it is an object of the present invention dispose the anode within ametallic enclosure mounted in the tube envelope, this enclosure having asmall aperture, and to dispose the cathode outside this enclosure atsuch position that the electron flow through the small aperture isinward rather than outward. In small hydrogen tubes, in which the windowmust necessarily be placed close to the small aperture, the window is 2prone to darken rather rapidly due to a deposit of metal or metaloxides. We have found that the particles causing the deposition travelfrom cathode to anode whereby, in conventional tubes,

these particles travel in a direction causing some proportion of them tofall on the window. In the modified inside-out construction hereindisclosed, such particles move in an opposite direction and tend todeposit on the metallic internal elements of the tube. This inside-outconstruction alone tends substantially to increase the life of smallhydrogen tubes by substantially preventing depositions on the windowfrom this source, but such reversal of anode and cathode will not, initself, eliminate some of the other difliculties to be hereinaftermentioned.

Extensive research has shown that the life of a small hydrogen tube inaffected by window depositions from other sources and by chemicalreactions within the tubeduring or prior to its operation, and it is anobject of the invention to minimize such depositions. The chemicalreactions responsible for the depositions have apparently not heretoforebeen recognized as taking place in hydrogen tubes. They may beclassified generally as water-forming and hydrogen-consuming reactions.

We have discovered that, even with the electron flow reversed, there isstill some tendency for the window to darken. The primary cause has beentraced to a disintegration of the tungsten usually employed to bound thesmall opening of the metallic enclosure. In this connection, a smallamount of water vapor may be present in the atmosphere of the tube dueto any one of the water-forming chemical reactions hereinaftermentioned. This water reacts slowly with the tungsten to form tungstenoxide which is vaporized at the existing temperature, the vapors beingcondensed on the cooler portions of the tube, including the window. Thisdisintegration of the tungsten bounding the small opening produces agradual enlargement of the opening.

It is known that atomic hydrogen can be formed by intense electricaldischarges in hydrogen gas, and we have found that this may occur inhydrogen tubes of the type with which the present invention isconcerned. Atomic hydrogen is a gas having an exceedingly high chemicalreactivity and it can combine with compounds otherwise stable tohydrogen, such as certain constituents of glass. It recombines to formmolecular hydrogen readily when in contact with metallic surfaces, butis relatively stable in the absence of a of the hydrogen atmosphere. torenew continuously or from time to time the surface on which therecombination can take place.

One of the objects of our invention is to expose I the gases which havevparticipated in.-the discharge to surfaces favoring the recombination ofhydride.

atomic into molecular hydrogen before the stream of gases comes v intointimate contact with the window or other surface of the glass envelopeof the tube on which deposits are undesirable. This It is also an objectof the present invention to provide a body of material which presents areaction surface to any atomic or ionic hydrogen in the tube to convertsuch atomic or ionic hydrogen may be achieved by employing a suitableshield, into molecular hydrogen and thus tend to prevent usuallyconnected to the metallic enclosure of the tube. to form a chimney todirect the hot gas stream from the discharge against a selected zone ofthe envelope, usually the upper interior surdisposed ballles. Any atomichydrogen or tungsten oxide vapors can thus be carried to a selectedportion of the enclosure to prevent promiscuous contact with otherportions thereof. The shield depletion of the hydrogen atmosphere. Afurther object is to dispose such material in protecting relationshipwith a glass envelope of a'hydrogen tube, particularly in a zone thereofmost likeface thereof, or against suitably constructed and ly to receivethe atomic or ionic hydrogen. Ifthe aforesaid shield is employed toestablish convection currents toward a selected zone of the envelope,the invention contemplates the placing of a coating of such material ontheenvelope in this m y also Prot ct the window against directradiazone. The aforesaid metal shield itself presents tion from thecathode. Such a shield may provide a larger aperture transmitting theradiation from the small aperture of the enclosure to the window. andcan be made to reduce the area of the an extensive surface which tendsto be contacted by such atomic or ionic hydrogen to cause recombinationinto molecular hydrogen at the surface of the shield. In some instanceswe have found glass envelope exposed to the arc. It is .an object itquite satisfactory to employ such an extensiveof the present inventionto provide a shield of this typ serving at least one of such functions.

Extensive experimentation with hydrogen tubes has shown that the amountof contained hydro,

gen tends to be reduced during operation of the tube. This isparticularly serious in small hydrogen tubes and, in many instances, hascaused failure of such tubes after a few hours of operation. It is animportant object of the present invention to provide a means within thehydrogen tube for reducing the rate of depletion of the hydrogen gas.

Any water-forming reaction within the tube will, of course, tend toconsume the hydrogen. For example, oxygen liberated from the metal partsof the tube or from contaminating oxides in the cathode coating willreact with hydrogen to cause its depletion.

In addition, low voltage thermionic tubes require the use of anoxide-coated filament, the coating being usually a mixture of barium andstrontium oxide. Molecular hydrogen will not appreciably react with andreduce such oxides but our investigation indicates that the oxidessurface shield in the production of long-lived tubes, even without thepreferred hydride coating, and such a construction is included among theobjects of the invention.

I It is also an object of the invention to provide novel methods ofmaking long-lived hydrogen tubes, including the step of insuringcomplete vaporization of a hydride-forming metal in the presence ofexcess hydrogen to prevent hydrogen- 5 consuming reactions after thetube is sealed.

Another object is to provide multiple metal-vaporizing steps to insurethis complete vaporization and conversion to the hydride.

Another object of the invention is to provide a vacuum tube having aglass envelope, a section of the glass itself being made thin to providethe window, thus avoiding the necessity of sealing quartz or fusedsilica windows to a glass envelope.

Further objects and advantages of the invention will be evident to thoseskilled in the art from the follower description of an exemplaryembodiment.

Referring to the drawing, in which the prereact with the activated formsof hydrogen, such ferred hydrogen tube is shown of a size approxasatomic hydrogen or various ionic forms which may be produced in thedischarge, with the production of water and metallic barium orstrontium. Thus, the reaction has two undesirable conimately double thatemployed in practice:

Fig. 1 is a vertical sectional view of the tube with the internal partsshown in elevation;

Fig. 2 is a vertical sectional view, taken on the sequences, theproduction of water and depletion line 2-2 of Fig. 1;

It is impractical hydrogen atmosphere, nor is it feasible, particularlyin small tubes, to employ enough hydrogen initially to prevent depletionin several hundred hours of operation.

We have found that the life of a hydrogen tube can be greatly increasedif it contains a chemical compound capable of reacting with water totake Fig. 3 is a horizontal sectional view, taken on the line 3-3 ofFig. 2; and

Fig. 4 is a side view of the internal elements of the tube, taken asindicated by the arrow 4 of Fig. 1.

up the oxygen and release the hydrogen, and it manufacturing process, isconnected to a suitable is an object of the invention to employ such acompound for this purpose, typically a metal hydride. In this way, theactual amount of hydrogen within the tube can be maintained subglasstube through which the envelope l0 may be evacuated or supplied with ahydrogen atmosphere. The lower indented end of the envelope l0 providesan element-supporting member l2 stantially constant or even increasedwith use of in which are sealed conductors l3 and It for supthe tube. Itis another object of the invention to deposit such a chemical compoundon internal surfaces of the tube by vaporizing a suitable metal in thetube, the vapors reacting with hydrogen plying filament current, andconductor I5 for supplying anode potential. That portion of theelement-supporting member I 2 around the conductor I5 is formed as ahead it. The conto form the hydride and these vapors condensing ductorsl3, l4, and I! are connected to suitable flexible leads or to the prongsof a suitable base, as desired.

A vertically-elongated portion ll of the glass envelope II is blownoutward during its manufacture and, after selective reheating, is suckedinward to form a window 26 of the general shape shown in Figs. 2 and 3.The window 20 is relatively thin as compared with the remaining walls ofthe glass envelope Ill. Very satisfactory results have been obtained byusing a glass particularly suited to the transmission of ultra violetradiation, e. 8., a glass known in the art as Corning No. 974. Thewindow 20 is usually made of a thickness of only about .005" to increasethe transparency to ultra violet radiation,.and the resulting window ispractically as transparent as a quartz window 1 mm. thick. Thisconstruction avoids the difficult problem of sealing separate windows tothe envelope.

Within the envelope In is a metal enclosure, best shown in Figs. 2, 3,and 4 and indicated generally by the numeral 25. This enclosure can beformed of tubular or sheet stock nickel bent to form a front wall 26,side Walls 21 and 28, and a rear wall 29, defining an upright space 30closed at its upper and lower ends by flanged plates 3i and 32. Theplate 32 provides an opening having a lip 33 which rests, on, and issupported by, the upper hemisphere of the bead l6. The enclosure 25 isalso supported by welding of the side wall 28 to the conductor H. Asmall tungsten plate 34 is spot welded to the front wall 26 at themidsection of the tube, and provides a small aperture 35 aligned with alarger opening of the wall, this small aperture serving to concentratethe electron flow.

Disposed in the enclosure 25, and preferably out of alignment with thesmall aperture 35, is an anode 31, conveniently a nickel plate welded tothe top of the conductor i and extending fore and aft of the tube.

The cathode, indicated generally by the numeral 40, is disposed outsidethe enclosure 25, preferably adjacent a corner thereof so as to bespaced from a line joining the window 20 and the small aperture 35.Preferably, this cathode is a narrow strip of metallic screen stretchedbetween upper and lower supports 4| and 42, respectively welded to theupper ends of conductors M and i3. correspondingly, one end of theoathode M is electrically connected to the enclosure iii. At least thecentral portion of the metallic screen is oxide coated to produceadequate electron emission when heated to relatively low temperatures, apreferred coating being a mixture of barium and strontium oxides. I

A member 45 is welded to the side walls 21 and 26 and provides a portionextending transversely of the tube between the front wall 26 and thewindow 20. This member 45 extends around the cathode 40 in a manner bestshown in Fig. 3. Its height is preferably equal to the height of theenclosure 25. A baiiie l6 divides the space bounded by the member 45 andthe enclosure 25 into an upright space 41 immediately in front of thefront wall 26 and an upright cathode-receiving space 48. Both uprightspaces are open at their upper and lower ends, and the temperaturetherein is such as to establish strong convection currents toward theupper interior of the glass envelope l0, thus serving to establishcirculation paths within the hydrogen atmosphere, indicated generally bythe arrows 49. The bailie 46 provides an aperture 50 near the midsectionof the cathode l0 and in horizontal alignment with the small aperture36. Similarly, the member 45 provides an aperture 52 substantiallylarger than the aperture 35 and disposed between the latter and thewindow 20 to frame the ultra violet radiation and confine this radiationto the central portion of the window 20. That portion of the member- 45extending forward from the side wall 21 and to the baiiie 46 ishereinafter referred to as a shield 55.

Extending upward from, and welded to, the rear wall 29 is an arm 58carrying a plate 59 concave toward the front of the glass envelope l0.Mounted on this plate is a small metal tab 60. This tab contains metalor substances forming metal on heating, which metal is adapted to bevaporized during manufacture of the hydrogen tube in a manner similar tothat employed in the vaporization of a getter in the manufacture of highvacuum tubes, namely, by inductive heating thereof from a position.outside the glass envelope Ill. The resulting vapors or reactionproducts thereof will move to the upper interior surface of the glassenvelope and condense to form a coating 62. Some advantages arise fromthe presence of this coating entirely aside from its composition. Forexample, any material coated on the upper interior of the glass envelopewill tend to form a protective surface therefor. Atomic or ionichydrogen, carried by the circulation indicated by arrows 49, willcontact such a coating 62 so that the atomic or ionic hydrogen will tendto recombine into molecular hydrogen. thus tending toprevent hydrogendepletion within the envelope.

However, itis particularly advantageous that this coating be a metalhydride. To produce such a coating, we prefer to vaporize, in a hydrogenatmosphere, a hydride-forming metal and the tab 60 may be composed of,or may include as a component, or may partially enclose, such a metal orsubstances adapted to produce such a metal. This metal may be either ahydrideforming alkali metal or alkaline earth metal. the latter beingdistinctly preferable as the alkali metal hydrides are quite volatileand tend quite rapidly to decompose to re-formthe alkali metal andliberate hydrogen at the operating temperature of the tube. Such alkalimetals can be em.- ployed in certain circumstances but the alkalineearth metals have been found generally superior for the intendedpurpose.

For example, if the small tab '60 is made of calcium, vaporizationthereof in a hydrogen atmosphere causes the vaporized calcium to reactwith the hydrogen to produce the hydride which deposits to form thecoating 62. Thereafter and during normal use of the tube, this calciumhydride is available to react with any water vapor present or formed,according to one or both of the following formulae:

' Reaction in accordance with Equation 1 is slow and that in accordancewith Equation. 2 predominates. A further reaction, though very slow asinvolving the reaction of two solids, may also be present, as follows:

Ca (OH) 2+CaH2- 2 Ca0+2H2 (3) Each of the above reactions ishydrogen-liberat ing and, in itself, tends actually to increase, duringuse of the tube, the total amount of gaseous hydrogen within the glassenvelope. We have than normal.

found that hydrogen-liberating reactions can be made to balance orover-balance other hydrogenconsuming reactions in the tube, particularlywhen the shield 55 is employed to establish con.- vection currentspreviously mentioned.

Similarly, strontium or barium can be employed as the hydride-formingalkaline earth metal and, from equations similar to those above, it willbe seen that any water vapor forming during operation of the tube willreact with the hy dride to renew, or prevent depletion of, the hydrogenatmosphere. It is important, however, that the hydride-forming metal ofthe tab 60 be completely vaporized. Our experience has shown that,unless this is done, the remaining metal may slowly react with thesealed-in hydrogen atmosphere in a manner tending to consume same.However, as will be later pointed out, it is not always essential thatall of the metal be vaporized in the presence of hydrogen during thetubemanufacturing process as some advantages can be derived from partialvaporization while the tube envelope is evacuated.

'In practice we prefer to employ as the small tab 60 an alloy of bariumwith magnesium and/or aluminum and to employ the following procedure inthe manufacture of the hydrogen tubes of the invention:

After the tube elements are in place and while the upper end of theglass envelope is connected to a suitable glass tube by which theenvelope and its elements can be supported, evacuated, or pressured withhydrogen, the envelope is exhausted by suitable means, usually by thecombined use of a mechanical vacuum pump and a diffusion pump, until theinternal pressure is about 10- mm. of Hg. The envelope is then filledwith hydrogen to a pressure of about one atmosphere and is surrounded byan electrically heated oven which brings its temperature to about 525C., after which it is cooled to about 345 C. This anneals and removesthe strains from the glass envelope. When the temperature drops to about345 C., the envelope is evacuated to about .05

mm. of Hg and the temperature is again raised to about 425 C. duringcontinued evacuation to an even lower pressure, thus baking out theglass and removing water vapor therefrom. The tube is then permitted tocool to about 400 C., with the vacuum applied, after which the oven isremoved.

The filament is then outgassed under vacuum ,while operating at a brightred heat, much higher Hydrogen is then admitted to the envelope and theinternal elements are heated to a red heat by an induction coilsurrounding the envelope to continue the outgassing operation. In thepreferred operation, the heat applied at this point is not sufficient tovaporize the metal of the tab 60. The envelope is then again evacuatedand the filament is further outgassed at a bright red heat in the mannernoted above.

Preparatory to vaporization of the small tab 80, hydrogen is admitted tothe envelope until the pressure is about 60 mm. of HE. A small inductionheater is then brought close to the back of the envelope adjacent thetab 60. The barium evaporates and forms barium hydride on its way to theupper interior wall of the glass envelope,

this hydride depositing on the glass to produce a' 'spongy deposit. Themagnesium in a bariummagnesium-aluminum alloy will also deposit but,during this first flash vaporization, most of the aluminum remains inthe tab 50. When the alloy in the tab contains no magnesium, the deposit8 at this time is almost invisible because most of the barium has beenreacted to form the colorless hydride.

It is important that all of the barium in the tab be evaporated andconverted into its hydride before the tube is placed in use. If this isnot done, the barium will continue to react with the hydrogen during useof the tube, it being understood that this reaction will be slow as onlythe barium on the relatively small surface of the tab would enter intothis reaction. While a small residual amount of barium will be convertedinto its hydride in the subsequently-mentioned aging step, it isdistinctly preferable to flash-vaporize substantially all of the bariumby induction heating.

It is preferable to have complete vaporization in the firstflash-vaporizing step, but this requires intense inductive heat appliedfor a sufficient length of time to insure such complete vaporization,and sometimes is difficult to accomplish in practice. To insure completevaporization of thebarium, we prefer to re-heat the tab to a highertemperature by re-application of the induction heater. In the preferredpractice, this is done after the envelope has been evacuated to aid ininsuring complete barium vaporization. The residual barium thusvaporized does not form a hydride during its movement to the interiorwall of the envelope but, instead, deposits as metallic barium on thepreviously-deposited spongy hydride coating. The observed result inpractice is that the coating now becomes substantially opaque, albeitthe coating is not necessarily continuous. The layer of metallic bariumis extremely thin and, because of the spongy nature of its foundationdeposit of hydride and also because of the relatively extensive area ofthe upper interior of the envelope, it presents a large surface area toany hydrogen later introduced into the tube, e. g., in thesubsequently-mentioned aging step, whereby the metallic barium iscompletely converted into hydride within a few hours and before sealingof! the envelope.

It is next preferred again to outgas the filament by heating it tohigher than normal temperature while the system is evacuated, aspreviously defined. Pure hydrogen gas is then introduced into theenvelope to a pressure of about 7.6 mm. of Hg. If the hydrogen is notpure, it is desirable to introduce it through a cold trap to condenseany condensabie material therein. The tube is then connected to a powersupply and aged for about 16 hours, while still connected to the sourceof hydrogen to replenish any of the hydrogen used up during the aging.During this aging step, any metallic barium in the coating 62 isconverted into its hydride. The tube is then sealed off and, after theusual tests, is ready for use.

As an alternative ofthe above procedure, involving flash vaporization ofthe barium in the tab 60 in the presence of a hydrogen atmosphere, it ispossible to vaporize all of the barium while/the envelope is evacuated.In this instance all of the barium deposits on the inner wall of theenvelope 'in a very thin coating and is entirely converted into itshydride in the later aging step when a continuously-replenished hydrogenatmosphere is present.

In the construction of the tube, we have found it very dfflicult toinsure complete vaporization of/ the hydride-forming metal if, forexample, the small tab 60 is placed on the exterior of the enclosure 25and if an attempt is made to vaporize the hydride-forming metal duringthe enclosure-heating step mentioned above. In this instance theapplication of sumciently high temperatures, by induction heating, toinsure vaporization of the hydride-forming metal is usually impracticalas it often results in partial or complete destruction or burning of theenclosure 25, usually formed of nickel, not to mention heating of theglass to such temperature that it will melt. Such problems are solved.by mounting the tab 50 at a position spaced from the enclosure 25 sothat it can be selectively heated to the flash-vaporizing temperature.The flag-like mounting of Figs. 1, 2, and 4 has been found particularlyeffective.

In the normal operation of the tube the electrons given oil from thecathode 40 move as a stream through the aperture 50 into the uprightspace ll, the stream turning therein and being confined by the smallaperture 35 and moving to the anode 31 through the upright space 30inside the enclosure 25. Without the shield, there will still be asubstantial tendency for the window 20 to darken due to th spattering oftungsten oxide from the aperture-forming plate 34 and for loss ofhydrogen to occur by reaction of the atomic or ionic form with the glassof the window. The presence of the shield 55 tends to prevent theseactions and the interior surface thereof tends to receive such tungstendeposits and also tends to provide a metallic surface contactable by theatomic or ionic hydrogen and on which recombination can take place tore-form molecular hydrogen. Such functions of the shield 55 are probablyaided by the upward thermally-induced flow of the hydrogen through theupright space 41. It is distinctly preferable that this upright spacehave its upper and lower ends open to the atmosphere of the tube. Tubeswith the internal construction shown and employing the shield 55 arelong lived, although it has been found that removal of the shield 55will substantially shorten the life of the tube, and these statementshold even though the tube does not contain a coating 62 of hydride ormetal on the surface of which the atomic or ionic hydrogen canrecombine.

On the other hand, the tube life can be additionally extended anddepletion of its hydrogen atmosphere further prevented by employment ofthe coating 52. This is true to some degree even if the coating 52 isformed of any protective material preventing contact of atomic or ionichydrogen with the glass of the envelope. It is true to a very markedextent if the coating 62 is a hydride, thereby replenishing the hydrogenatmosphere, and in some instances even increasing the amount ofhydrogen, during operation of the tube.

Various changes and modifications can be made without departing from thespirit of the invention as defined in the appended claims.

We claim as our invention:

1. In a long-lived hydrogen tube, the combination of: an envelopeproviding a window for passage of ultra violet radiation, the "interiorof said envelope containing hydrogen gas; an enclosure within saidenvelope and providing a wall having a small aperture facing saidwindow; an anode within said enclosure and on one side of said wall; acathode outside said enclosure to be on the other side of said wall andadapted when heated to produce an electron stream moving inward throughsaid aperture and to said anode; said electron flow tending to produceactivated hydrogen reactable with the material of said window; and meanswithin said envelope for converting said activated hydrogen intomolecular hydrogen to avoid such reaction with the material of saidwindow and to prevent depletion of said hydrogen gas.

2. A hydrogen tube as defined in claim 1, in which said small apertureis bounded by tungsten which tends to disintegrate and form a deposit onsaid window, and including a shield electrically connected to saidenclosure for preventing such deposition on said window, said shieldproviding an aperture aligned with said small aperture of said enclosurefor transmitting the radiation to said window.

3. In a long-lived hydrogen tube, the combination of: an envelopeproviding a window for passage of ultra violet radiation, the interiorof said envelope containing hydrogen gas; an enclosure within saidenvelope and providing a wall having a small aperture facing saidwindow; an anode within said enclosure on one side of said wall; acathode outside said enclosure to be on the other side of said wall andadapted when heated to produce an electron stream moving inward throughsaid aperture and to said anode. said cathode being disposed to one sideof a line joining said aperture and said window; and a shield having anaperture larger than said small aperture and disposed between saidwindow and said small aperture.

4. In a long-lived hydrogen tube, the combination of: an envelopeproviding a window for passage of ultra violet radiation, the interiorof said envelope containing hydrogen gas; means for'establishing anelectron flow through said hydrogen gas and for confining said electronflow opposite said window to produce intense ultra violet radiation,said electron flow tending'to produce atomic hydrogen; and means forpreventing depletion of said hydrogen gas during use of said tube, saidmeans including a surface exposed to said hydrogen gas and to saidatomic hydrogen within said tube and on which said atomic hydrogenreacts with itself to produce molecular hydrogen.

5. A hydrogen tube as defined in claim 4,-ineluding means for guidingsuch atomic hydrogen to said surface.

6. A hydrogen tube as defined in claim 4, in which said envelope isglass whereby said atomic hydrogen tends to react therewith, and inwhich said surface comprises a layer of inert material not reactablewith molecular hydrogen, said layer covering at least a portion of theinner surface of said glass.

'7. In a long-lived hydrogen tube, the combination of: a glass envelopeproviding a window for passage of ultra violet radiation, the interiorof said glass envelope containing hydrogen gas; means for establishingan electron flow through said hydrogen gas of sufficient intensity topro duce said ultra violet radiation and toproduce atomic hydrogen andthus tending to deplete the amount of hydrogen gas in said glassenvelope; means for establishing a thermal circulation in said hydrogengas from the vicinity of said electron flow and toward a selected zoneof said glass envelope to carry atomic hydrogen toward said zone; and abody of material incapable of reaction with atomic hydrogen and disposedin the circulating hydrogen gas at a position to shield said zone ofsaid glass envelope from substantial contact with the atomic hydrogen inthe stream of circulating hydrogen gas, said material providing asurface contacted by said stream and on which the atomic hydrogencombines with itself to re-form molecular hydrogen and thus diminishdepletion of said hydrogen gas.

8. A hydrogen tube as defined in claim 7, in which said body of materialis a coating on the inside of said glass envelope occupying said zonethereof. 1

9. A hydrogen tube as defined in claim 7, in

which said material is a metal hydride capable 'to react with andliberate hydrogen when contacted by any water resulting fromwater-forming chemical reactions in said tube, said tube being furthercharacterized by the substantial absence of any hydride-forming metal incontact with the hydrogen gas within said envelope and which would reactwith such hydrogen during operation of the tube.

11. As an article of manufacture, a long-lived hydrogen tube includingin combination: an envelope providing a window for passage of ultraviolet radiation, the interior of said envelope containing hydrogen gas;an enclosure within said envelope and providing a wall having a smallaperture facing said window; an anode and a cathode on opposite sides ofsaid wall and adapted to produce an electron stream moving through saidaperture; and a vapor-deposited coating of metal hydride covering aportion of the interior of said envelope, said tube being furthercharacterized by the substantial absence of any hydride-forming metal incontact with the hydrogen gas within said envelope and which would reactwith such hydrogen during operation of the tube.

12. As an article of manufacture: an envelope providing a window forpassage of ultra violet radiation, the interior of said envelope beingadapted to contain hydrogen gas; an enclosure within said envelope andproviding a wall havinga small aperture facing said window; an anode anda cathode on opposite sides of said wall and adapted to produce anelectron stream moving through said aperture; a small body ofhydrideforming metal within said enclosure and selected from the classconsisting of hydride-forming alkali metals and hydride-forming alkalineearth metals; and means for mounting said small body of hydride-formingmetal in spaced relationship with said enclosure and sufiiciently closeto said envelope to be completely vaporized by induction heating throughsaid envelope whereby such heating will vaporize said hydride-formingmetal and the resulting vapors will react with the hydrogen within saidenclosure to form a hydride of said metal, said hydridedepositing on theinterior surface of said envelope.

13. As an article of manufacture, a long-lived hydrogen tube includingin combination: an envelope providing a window for passage of ultraviolet radiation, the interior of said envelope containing hydrogen gas;an enclosure within said envelope and providing a wall Having a smallaperture facing said window; an anode within said enclosure and on oneside of said wall; a cathode outside said enclosure to be on the otherside of said wall and adapted when heated to produce an electron streammoving inward through said aperture to said anode; a shield between saidwall and said window and spaced from said wall to define an uprightspace open at its upper and lower ends, said shield providing anaperture framing the ultra violet radiation moving toward said window;and a coating of a metal hydride covering the upper interior of saidenvelope to be disposed in the path of a stream of hydrogen gas risingin said upright space, said tube being further characterized by thesubstantial absence of any hydride-forming metal in contact with thehydrogen gas within said envelope and which would react with suchhydrogen during operation of the tube.

14. A long-lived hydrogen tube as defined in claim 3 in which saidenclosure is formed of meta1, and in which said shield is also formed ofmetal and is electrically connected to said enclosure.

15. A long-lived hydrogen tube as defined in claim 3 in which saidshield provides a space open at its upper and lower ends to the hydrogengas in said envelope, said electron flow establishing a discharge movingthrough said space to heat the gas therein, the heated gas tending torise in said space, said discharge tending to produce activatedhydrogen, and in which said shield provides an extensive-area surface onwhich such activated hydrogen recombines to form molecular hydrogen.

16. In a long-lived hydrogen tube, the combination of an envelopeproviding a window for passage of ultra violet radiation, the interiorof said envelope containing a body of hydrogen; means for establishingan electron flow through said hydrogen to produce ultra violetradiation; and means for preventing depletion of said hydrogen becauseof any water-forming reactions within said envelope, said meansincluding means for establishing a thermal circulation in said body ofhydrogen gas from the zone of said electron flow to a. selected zoneinside said envelope and spaced from said window to carry to saidselected zone any water in the circulating hydrogen, said last-namedmeans including a metal hydride in the path of said circulating hydrogento react with such water and release hydrogen.

HENRY H. CARY. WARREN P. BAXTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,917,848 Marden et a1 July 11,1933 1,922,281 Dawson Aug. 15, 1933 1,991,479 Williams Feb. 19, 19351,999,653 Case Apr. 30, 1935 2,047,175 Braselton July 14, 1936 2,162,505James et al June 13, 1939

